A power supply converter converts an input voltage into an output voltage having a prescribed voltage value, and outputs the output voltage to a load circuit. Such a power supply converter has, for example, a switching circuit with a high-withstanding-voltage switching transistor which turns the current flowing in a coil on and off, and a control circuit which controls the switching circuit such that the output voltage is at a desired potential. The input voltage is for example a commercial power supply, and the output voltage is for example an extremely high DC voltage such as 380 V. Hence the switching transistor within this switching circuit is a high-withstanding-voltage transistor which withstand high voltages.
The control circuit generates a control signal to drive the switching transistor such that the output voltage is the desired voltage. For example, when the output voltage is lower than the reference voltage, the switching transistor is made to conduct for a longer time, increasing the energy of the coil, whereas when the output voltage is higher than the reference voltage, the switching transistor is made to conduct for a shorter time, decreasing the energy of the coil. In this way, by controlling the on and off times of the switching transistor with high precision, the output voltage is precisely controlled at the desired voltage.
Such a power supply converter is for example described in Japanese Patent Application Laid-open No. H01-255263 and Japanese Patent Application Laid-open No. 2010-220330.
As explained above, the switching transistor in a switching circuit is required to withstand high voltages, and so use of compound semiconductor transistors of SiC, GaN and similar, rather than silicon semiconductor transistors, is proposed.
However, a high-voltage switching transistor switches large currents on and off each time switching occurs. Accompanying this, due to the parasitic inductance resulting from wiring on the semiconductor chip on which the switching transistor is formed, the bonding wire connecting between electrodes of package accommodating the semiconductor chip and electrode pads on the semiconductor chip, and similar, when a large current is switched from on to off a negative potential appears at the source terminal of the switching transistor, and there are cases in which an erroneous operation in which the switching transistor is inverted from off to on occurs. Such erroneous operation means that the turn-off operation of the switching transistor is not performed with high precision.